Trypsin-catalysed formation of pig des-(23-63)-proinsulin from desoctapeptide-(B23-30)-insulin

Incubation of pig desoctapeptide-(B23-30)-insulin with trypsin in solvent systems consisting of dimethyl sulphoxide, butane-1,4-diol and Tris buffer resulted in the formation of an extra peptide bond between Arg-B22 and Gly-A1 in the DOPI molecule. This DOPI derivative can also be regarded as pig des-(23-63)-proinsulin. The structure of the new, previously unreported, proinsulin analogue was determined on the basis of amino acid analysis, dansylation and digestion with Staphylococcus aureus V8 proteinase. Receptor-binding ability of des-(23-63)-proinsulin was 20% of that of pig desoctapeptide-(B23-30)-insulin and 0.02% of that of pig insulin.